/*
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* Copyright (C) 2018 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#define LOG_TAG "PrivateDnsConfiguration"
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#define DBG 0
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#include "PrivateDnsConfiguration.h"
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#include <log/log.h>
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#include <netdb.h>
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#include <sys/socket.h>
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#include "DnsTlsTransport.h"
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#include "ResolverEventReporter.h"
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#include "netd_resolv/resolv.h"
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#include "netdutils/BackoffSequence.h"
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namespace android {
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namespace net {
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std::string addrToString(const sockaddr_storage* addr) {
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char out[INET6_ADDRSTRLEN] = {0};
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getnameinfo((const sockaddr*) addr, sizeof(sockaddr_storage), out, INET6_ADDRSTRLEN, nullptr, 0,
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NI_NUMERICHOST);
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return std::string(out);
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}
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bool parseServer(const char* server, sockaddr_storage* parsed) {
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addrinfo hints = {.ai_family = AF_UNSPEC, .ai_flags = AI_NUMERICHOST | AI_NUMERICSERV};
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addrinfo* res;
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int err = getaddrinfo(server, "853", &hints, &res);
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if (err != 0) {
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ALOGW("Failed to parse server address (%s): %s", server, gai_strerror(err));
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return false;
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}
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memcpy(parsed, res->ai_addr, res->ai_addrlen);
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freeaddrinfo(res);
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return true;
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}
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int PrivateDnsConfiguration::set(int32_t netId, uint32_t mark,
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const std::vector<std::string>& servers, const std::string& name,
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const std::set<std::vector<uint8_t>>& fingerprints) {
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if (DBG) {
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ALOGD("PrivateDnsConfiguration::set(%u, 0x%x, %zu, %s, %zu)", netId, mark, servers.size(),
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name.c_str(), fingerprints.size());
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}
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const bool explicitlyConfigured = !name.empty() || !fingerprints.empty();
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// Parse the list of servers that has been passed in
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std::set<DnsTlsServer> tlsServers;
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for (size_t i = 0; i < servers.size(); ++i) {
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sockaddr_storage parsed;
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if (!parseServer(servers[i].c_str(), &parsed)) {
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return -EINVAL;
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}
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DnsTlsServer server(parsed);
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server.name = name;
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server.fingerprints = fingerprints;
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tlsServers.insert(server);
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}
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std::lock_guard guard(mPrivateDnsLock);
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if (explicitlyConfigured) {
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mPrivateDnsModes[netId] = PrivateDnsMode::STRICT;
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} else if (!tlsServers.empty()) {
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mPrivateDnsModes[netId] = PrivateDnsMode::OPPORTUNISTIC;
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} else {
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mPrivateDnsModes[netId] = PrivateDnsMode::OFF;
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mPrivateDnsTransports.erase(netId);
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return 0;
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}
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// Create the tracker if it was not present
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auto netPair = mPrivateDnsTransports.find(netId);
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if (netPair == mPrivateDnsTransports.end()) {
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// No TLS tracker yet for this netId.
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bool added;
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std::tie(netPair, added) = mPrivateDnsTransports.emplace(netId, PrivateDnsTracker());
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if (!added) {
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ALOGE("Memory error while recording private DNS for netId %d", netId);
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return -ENOMEM;
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}
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}
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auto& tracker = netPair->second;
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// Remove any servers from the tracker that are not in |servers| exactly.
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for (auto it = tracker.begin(); it != tracker.end();) {
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if (tlsServers.count(it->first) == 0) {
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it = tracker.erase(it);
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} else {
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++it;
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}
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}
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// Add any new or changed servers to the tracker, and initiate async checks for them.
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for (const auto& server : tlsServers) {
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if (needsValidation(tracker, server)) {
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validatePrivateDnsProvider(server, tracker, netId, mark);
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}
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}
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return 0;
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}
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PrivateDnsStatus PrivateDnsConfiguration::getStatus(unsigned netId) {
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PrivateDnsStatus status{PrivateDnsMode::OFF, {}};
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std::lock_guard guard(mPrivateDnsLock);
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const auto mode = mPrivateDnsModes.find(netId);
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if (mode == mPrivateDnsModes.end()) return status;
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status.mode = mode->second;
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const auto netPair = mPrivateDnsTransports.find(netId);
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if (netPair != mPrivateDnsTransports.end()) {
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for (const auto& serverPair : netPair->second) {
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if (serverPair.second == Validation::success) {
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status.validatedServers.push_back(serverPair.first);
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}
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}
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}
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return status;
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}
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void PrivateDnsConfiguration::getStatus(unsigned netId, ExternalPrivateDnsStatus* status) {
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std::lock_guard guard(mPrivateDnsLock);
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const auto mode = mPrivateDnsModes.find(netId);
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if (mode == mPrivateDnsModes.end()) return;
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status->mode = mode->second;
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const auto netPair = mPrivateDnsTransports.find(netId);
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if (netPair != mPrivateDnsTransports.end()) {
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int count = 0;
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for (const auto& serverPair : netPair->second) {
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status->serverStatus[count].ss = serverPair.first.ss;
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status->serverStatus[count].hostname =
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serverPair.first.name.empty() ? "" : serverPair.first.name.c_str();
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status->serverStatus[count].validation = serverPair.second;
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count++;
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if (count >= MAXNS) break; // Lose the rest
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}
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status->numServers = count;
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}
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}
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void PrivateDnsConfiguration::clear(unsigned netId) {
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if (DBG) {
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ALOGD("PrivateDnsConfiguration::clear(%u)", netId);
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}
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std::lock_guard guard(mPrivateDnsLock);
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mPrivateDnsModes.erase(netId);
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mPrivateDnsTransports.erase(netId);
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}
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void PrivateDnsConfiguration::validatePrivateDnsProvider(const DnsTlsServer& server,
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PrivateDnsTracker& tracker, unsigned netId,
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uint32_t mark) REQUIRES(mPrivateDnsLock) {
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if (DBG) {
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ALOGD("validatePrivateDnsProvider(%s, %u)", addrToString(&server.ss).c_str(), netId);
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}
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tracker[server] = Validation::in_process;
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if (DBG) {
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ALOGD("Server %s marked as in_process. Tracker now has size %zu",
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addrToString(&server.ss).c_str(), tracker.size());
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}
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// Note that capturing |server| and |netId| in this lambda create copies.
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std::thread validate_thread([this, server, netId, mark] {
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// cat /proc/sys/net/ipv4/tcp_syn_retries yields "6".
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//
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// Start with a 1 minute delay and backoff to once per hour.
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//
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// Assumptions:
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// [1] Each TLS validation is ~10KB of certs+handshake+payload.
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// [2] Network typically provision clients with <=4 nameservers.
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// [3] Average month has 30 days.
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//
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// Each validation pass in a given hour is ~1.2MB of data. And 24
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// such validation passes per day is about ~30MB per month, in the
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// worst case. Otherwise, this will cost ~600 SYNs per month
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// (6 SYNs per ip, 4 ips per validation pass, 24 passes per day).
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auto backoff = netdutils::BackoffSequence<>::Builder()
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.withInitialRetransmissionTime(std::chrono::seconds(60))
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.withMaximumRetransmissionTime(std::chrono::seconds(3600))
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.build();
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while (true) {
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// ::validate() is a blocking call that performs network operations.
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// It can take milliseconds to minutes, up to the SYN retry limit.
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const bool success = DnsTlsTransport::validate(server, netId, mark);
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if (DBG) {
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ALOGD("validateDnsTlsServer returned %d for %s", success,
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addrToString(&server.ss).c_str());
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}
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const bool needs_reeval = this->recordPrivateDnsValidation(server, netId, success);
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if (!needs_reeval) {
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break;
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}
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if (backoff.hasNextTimeout()) {
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std::this_thread::sleep_for(backoff.getNextTimeout());
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} else {
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break;
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}
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}
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});
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validate_thread.detach();
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}
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bool PrivateDnsConfiguration::recordPrivateDnsValidation(const DnsTlsServer& server, unsigned netId,
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bool success) {
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constexpr bool NEEDS_REEVALUATION = true;
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constexpr bool DONT_REEVALUATE = false;
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std::lock_guard guard(mPrivateDnsLock);
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auto netPair = mPrivateDnsTransports.find(netId);
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if (netPair == mPrivateDnsTransports.end()) {
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ALOGW("netId %u was erased during private DNS validation", netId);
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return DONT_REEVALUATE;
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}
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const auto mode = mPrivateDnsModes.find(netId);
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if (mode == mPrivateDnsModes.end()) {
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ALOGW("netId %u has no private DNS validation mode", netId);
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return DONT_REEVALUATE;
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}
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const bool modeDoesReevaluation = (mode->second == PrivateDnsMode::STRICT);
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bool reevaluationStatus =
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(success || !modeDoesReevaluation) ? DONT_REEVALUATE : NEEDS_REEVALUATION;
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auto& tracker = netPair->second;
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auto serverPair = tracker.find(server);
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if (serverPair == tracker.end()) {
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ALOGW("Server %s was removed during private DNS validation",
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addrToString(&server.ss).c_str());
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success = false;
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reevaluationStatus = DONT_REEVALUATE;
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} else if (!(serverPair->first == server)) {
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// TODO: It doesn't seem correct to overwrite the tracker entry for
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// |server| down below in this circumstance... Fix this.
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ALOGW("Server %s was changed during private DNS validation",
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addrToString(&server.ss).c_str());
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success = false;
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reevaluationStatus = DONT_REEVALUATE;
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}
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// Send a validation event to NetdEventListenerService.
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const auto& listeners = ResolverEventReporter::getInstance().getListeners();
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if (listeners.size() != 0) {
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for (const auto& it : listeners) {
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it->onPrivateDnsValidationEvent(netId, addrToString(&server.ss), server.name, success);
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}
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if (DBG) {
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ALOGD("Sent validation %s event on netId %u for %s with hostname %s",
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success ? "success" : "failure", netId, addrToString(&server.ss).c_str(),
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server.name.c_str());
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}
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} else {
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ALOGE("Validation event not sent since no INetdEventListener receiver is available.");
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}
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if (success) {
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tracker[server] = Validation::success;
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if (DBG) {
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ALOGD("Validation succeeded for %s! Tracker now has %zu entries.",
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addrToString(&server.ss).c_str(), tracker.size());
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}
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} else {
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// Validation failure is expected if a user is on a captive portal.
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// TODO: Trigger a second validation attempt after captive portal login
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// succeeds.
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tracker[server] = (reevaluationStatus == NEEDS_REEVALUATION) ? Validation::in_process
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: Validation::fail;
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if (DBG) {
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ALOGD("Validation failed for %s!", addrToString(&server.ss).c_str());
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}
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}
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return reevaluationStatus;
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}
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// Start validation for newly added servers as well as any servers that have
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// landed in Validation::fail state. Note that servers that have failed
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// multiple validation attempts but for which there is still a validating
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// thread running are marked as being Validation::in_process.
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bool PrivateDnsConfiguration::needsValidation(const PrivateDnsTracker& tracker,
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const DnsTlsServer& server) {
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const auto& iter = tracker.find(server);
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return (iter == tracker.end()) || (iter->second == Validation::fail);
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}
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PrivateDnsConfiguration gPrivateDnsConfiguration;
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} // namespace net
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} // namespace android
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